The invention relates to casters in general, and more particularly to improvements in casters with brakes for their wheels. Such casters can be used on the legs of tables, chairs, beds, scaffolds and many other mobile structures.
It is already known to provide a caster with a support which can be removably or permanently secured to the leg of a table, chair or other mobile structure and carries a swivel bearing for the web of an inverted U-shaped frame having two legs which flank a wheel and support the ends of a shaft defining a horizontal axis for the wheel. The swivel bearing enables the frame to turn about a substantially vertical axis.
It is also known to provide a caster with a brake which can be actuated to prevent rotation of the wheel about the horizontal axis and to simultaneously prevent turning of the wheel frame about the vertical axis. To this end, the legs of the frame have slots for the shaft which supports the wheel, and the frame pivotably supports a pedal which can be moved relative to the frame to displace the shaft in the slots of the legs to a position in which the wheel frictionally engages and displaces a brake into frictional engagement with the wheel frame.
Published German patent application No. 34 26 443 discloses a caster wherein the support includes an upright stud the lower end portion of which carries two races flanking the web of the inverted U-shaped wheel frame. Rolling elements are disposed between the web and each of the two races in order to reduce friction and to permit the frame and the wheel to turn about the vertical axis of the stud. The downwardly extending legs of the frame flank the wheel and have slots for the shaft which supports and defines a horizontal axis for the wheel. The legs of the wheel frame pivotably support the arms of a pedal which has cam slots crossing the slots of the respective legs and receiving portions of the shaft. When the pedal is depressed, the surfaces bounding its slots displace the shaft in the slots of the legs to a position in which the axis of the wheel crosses the axis of the stud and the wheel is held against rotation about its axis. When the pedal is moved to an inoperative position, the axis of the wheel is laterally offset with reference to the axis of the stud and the wheel is free to rotate about its own axis which is located behind the axis of the stud when the mobile structure utilizing the caster is set in motion. The wheel frame of the just described caster does not move in response to movement of the shaft in the slots of the two legs. The means for holding the wheel against rotation in response to depression of the pedal includes a brake which is fixed to the legs of the wheel frame and is engaged by the wheel in response to depression of the pedal. A drawback of this caster is that any play between the races of the swivel bearing can affect the stability of the mobile structure, especially if the latter is a tall scaffold or a working platform serving to support workers and/or equipment at a considerable distance from the ground.